What is Thematic Mapping?

In contrast to general ones, thematic maps emphasize on geographic areas of a particular region for data analysis. These charts provide information or data related to the percentage unemployed, the population explosion, and climate or soil type of a particular area. They are also known as graphic essays, that use 'base data' of places and coastlines as a reference point.

The use of thematic mapping can be traced back to 1686, when Edmond Halley, an English astronomer published a plan called the terrestrial map. He featured it in his article about trade winds. This was the earliest meteorological chart that came into being.

The use of thematic mapping became prominent in 1854, when John Snow, a physician from London, used thematic principles to devise a chart to analyze the spread of cholera in a particular area.

His method of mapping included the use of Geographic Information System, which comprised locations of pumps and streets in the neighborhood of London. The outbreak of cholera was mapped, and the emerging pattern directed to a pump located on Broad Street. With the removal of the pump it was revealed that a sewer line was passing beside it.

Thematic charts provide location-specific information. Charts consisting of demographic data of the density of population are good examples. In terms of designing a thematic chart, spatial patterns and detailed visual perception, along with the presentation, should be taken into consideration.

Like the name suggests, these charts use symbols that vary in size to denote a particular region. The symbols used vary in accordance with the proportion of quantities represented by the symbol. A symbol adds to the effectiveness of a chart.

Choropleth charts make visualization of a particular area relatively easy. If you consider the population of a certain region, you can use color as a symbol for that region. Areas with less population can be shaded with a light color, whereas densely populated areas can be shaded using darker colors.

These charts explore the possibilities of using two variables on a single chart. It can be a combination of sets of colors or symbols. Determining the population density and rainfall in a particular region could be the two variables. You can denote symbols or colors for the two variables.

As the name suggests the symbol used to denote an occurrence is a dot. The dots used should be uniform in appearance. For example, a cluster of dots can represent multiple entities. In case of multiple entities different colors are used.

These charts simplify data with the help of continuous distribution. They are used for mapping atmospheric pressure and environmental data. Lines are used to connect points which represent a certain value.

Dasymetric charts depict quantitative volumetric data of a particular area. They are extensively used by cartographers for mapping population density. They use standardized data. These became popular, as they provided methods for accurate and detailed visualization, for mapping population density.

Thematic charts act as an important reference tool, and are used for mapping frequent occurrences of geographical concepts, such as density or climate, in a particular region.